Fix SOA RNAME email local-part encoding

src/DNS/Message/Domain.php

@@ -31,7 +31,7 @@ public static function encode(string $name): string
             return "\x00";
         }
 
-        $labels = explode('.', $trimmed);
+        $labels = self::splitLabels($trimmed);
         $labelCount = count($labels);
 
         if ($labelCount > self::MAX_LABELS) {
@@ -71,6 +71,53 @@ public static function encode(string $name): string
         return $encoded . "\x00";
     }
 
+    /**
+     * Split a presentation-format domain name into labels.
+     *
+     * Escaped dots represent literal dots inside a label, as used by SOA RNAME
+     * mailbox local parts such as "first\.last.example.com".
+     *
+     * @return list<string>
+     */
+    private static function splitLabels(string $name): array
+    {
+        $labels = [];
+        $label = '';
+        $length = strlen($name);
+        $escaped = false;
+
+        for ($i = 0; $i < $length; $i++) {
+            $char = $name[$i];
+
+            if ($escaped) {
+                $label .= $char;
+                $escaped = false;
+                continue;
+            }
+
+            if ($char === '\\') {
+                $escaped = true;
+                continue;
+            }
+
+            if ($char === '.') {
+                $labels[] = $label;
+                $label = '';
+                continue;
+            }
+
+            $label .= $char;
+        }
+
+        if ($escaped) {
+            $label .= '\\';
+        }
+
+        $labels[] = $label;
+
+        return $labels;
+    }
+
     /**
      * Decode a domain name from DNS wire format, handling compression pointers.
      *

src/DNS/Message/Record.php

@@ -514,6 +514,7 @@ private function encodeSoaRdata(): string
         }
 
         [$mname, $rname, $serial, $refresh, $retry, $expire, $minimum] = $parts;
+        $rname = self::normalizeSoaRname($rname);
 
         $numbers = [];
         foreach ([$serial, $refresh, $retry, $expire, $minimum] as $value) {
@@ -535,6 +536,49 @@ private function encodeSoaRdata(): string
             . pack('NNNNN', $serialNum, $refreshNum, $retryNum, $expireNum, $minimumNum);
     }
 
+    private static function normalizeSoaRname(string $rname): string
+    {
+        if (!str_contains($rname, '@')) {
+            return $rname;
+        }
+
+        [$localPart, $domain] = explode('@', $rname, 2);
+
+        return self::escapeSoaRnameLocalPart($localPart) . '.' . $domain;
+    }
+
+    private static function escapeSoaRnameLocalPart(string $localPart): string
+    {
+        $escaped = '';
+        $length = strlen($localPart);
+        $isEscaped = false;
+
+        for ($i = 0; $i < $length; $i++) {
+            $char = $localPart[$i];
+
+            if ($isEscaped) {
+                $escaped .= $char;
+                $isEscaped = false;
+                continue;
+            }
+
+            if ($char === '\\') {
+                $escaped .= $char;
+                $isEscaped = true;
+                continue;
+            }
+
+            if ($char === '.') {
+                $escaped .= '\\.';
+                continue;
+            }
+
+            $escaped .= $char;
+        }
+
+        return $escaped;
+    }
+
     private function encodeCaaRdata(): string
     {
         $input = trim($this->rdata);

tests/unit/DNS/Message/DomainTest.php

@@ -24,6 +24,13 @@ public function testEncodeTreatsSingleTrailingDotAsAbsolute(): void
         );
     }
 
+    public function testEncodeTreatsEscapedDotAsLiteralLabelCharacter(): void
+    {
+        $encoded = Domain::encode('first\.last.example.com');
+
+        $this->assertSame("\x0Afirst.last\x07example\x03com\x00", $encoded);
+    }
+
     public function testEncodeAllowsRootViaEmptyString(): void
     {
         $this->assertSame("\x00", Domain::encode(''));

tests/unit/DNS/Message/RecordTest.php

@@ -295,6 +295,36 @@ class: Record::CLASS_IN,
         $this->assertSame($expected, $record->encode());
     }
 
+    public function testEncodeSoaRecordAcceptsEmailRname(): void
+    {
+        $record = new Record(
+            name: 'example.com',
+            type: Record::TYPE_SOA,
+            class: Record::CLASS_IN,
+            ttl: 3600,
+            rdata: 'ns1.example.com hostmaster@example.com 2024102701 7200 3600 1209600 86400'
+        );
+
+        $encoded = $record->encode();
+
+        $this->assertStringContainsString("\x0Ahostmaster\x07example\x03com\x00", $encoded);
+    }
+
+    public function testEncodeSoaRecordEscapesDotsInEmailRnameLocalPart(): void
+    {
+        $record = new Record(
+            name: 'example.com',
+            type: Record::TYPE_SOA,
+            class: Record::CLASS_IN,
+            ttl: 3600,
+            rdata: 'ns1.example.com first.last@example.com 2024102701 7200 3600 1209600 86400'
+        );
+
+        $encoded = $record->encode();
+
+        $this->assertStringContainsString("\x0Afirst.last\x07example\x03com\x00", $encoded);
+    }
+
     public function testDecodeTxtRecordWithMultipleChunks(): void
     {
         // TXT with two chunks: "hello" (5 bytes) + "world" (5 bytes)

tests/unit/DNS/Zone/FileTest.php

@@ -202,6 +202,20 @@ public function testImportUsesDefaultOriginWhenDirectiveMissing(): void
         $this->assertSame('www.example.com', $zone->records[0]->name);
     }
 
+    public function testImportAllowsEmailAddressSoaRnameToEncode(): void
+    {
+        $contents = <<<'ZONE'
+@ IN SOA ns1.example.com. first.last@example.com. 2025011801 7200 3600 1209600 1800
+www 600 IN A 192.0.2.10
+ZONE;
+
+        $zone = File::import($contents, 'example.com');
+
+        $encoded = $zone->soa->encode();
+
+        $this->assertStringContainsString("\x0Afirst.last\x07example\x03com\x00", $encoded);
+    }
+
     public function testImportFailsWhenSoaDataMissing(): void
     {
         $this->expectException(ImportException::class);